The invention relates to a half-bridge module for the switching of electrical outputs, which is arranged in a housing containing an electrically insulating cooling liquid and in which at least two semiconductor switches are connected in series, forming a half-bridge. Each semiconductor switch comprises a control input for connection to a triggering device. The first semiconductor switch is capable of being connected by its source terminal to a high voltage potential, and the second semiconductor switch is capable of being connected by its drain terminal to a low voltage potential. For the purpose of forming an output, the drain terminal of each first semiconductor switch is connected to the source terminal of the respective second semiconductor switch. In addition, at least one capacitor arrangement is arranged between the high voltage potential and the low voltage potential. Such a half-bridge module is known from German Patent Publication DE-A-42 30 510.
Half-bridge arrangements of such a type are used for the purpose of forming inverters for highly diverse fields of application, e.g. for feeding induction machines, permanent-magnet motors and similar applications. (See also, for example, German Patent Publication DE-A-40 27 969).
From U.S. Pat. No. 5,132,896 an inverter arrangement is known which, with a view to reducing the effect of distributed inductances of the conductors that are used for connecting the capacitors and the semiconductor switches, comprises lamellar supply lines having a large area. By this means, large damping capacitors for compensating the line inductances are avoided. In addition, the dissipation of heat can be improved by virtue of the large-area design of the lamellar supply lines. Furthermore, the lamellar supply lines are designed in such a way that the magnitude and the direction of the current flow through the lamellar supply lines minimizes the effect of the distributed inductances.
However, with this inverter arrangement the large-area supply lines serve merely to lessen interfering inductances and are employed as supply lines leading to large electrolytic capacitors.
In order to increase further the power density of the half-bridge module described in the introduction and in order to make it still more suitable, in particular, for large-scale use the half-bridge module claimed herein has been developed such that respective first semiconductor switches are arranged with their source terminal on a common first metallic conductor rail which is capable of being connected to the high voltage potential, and respective second semiconductor switches are arranged with their source terminal on a common second metallic conductor rail constituting the output, the second conductor rail being arranged alongside the first conductor rail, spaced therefrom. Moreover, each second semiconductor switch is connected by its drain terminal to a common third metallic conductor rail which is capable of being connected to the low voltage potential and is arranged alongside the first and second conductor rails, spaced therefrom. The capacitor arrangement comprises a backup capacitor which is connected to the first and third conductor rails by terminals and which overlaps the first and second semiconductor switches in such a manner that the semiconductor switches are spatially located between the corresponding conductor rails and the backup capacitor. In addition, the control input comprises a terminal for connection to the triggering device in the region of a first front side of the conductor rails, and the output comprises a terminal for connection to an electrical load in the region of a second front side of the second conductor rail located opposite the first front side.
By virtue of the structure, according to the present invention, of the half-bridge module, a particularly compact arrangement is achieved which enables a packaging density that cannot be equalled by previous solutions. As a consequence, the requisite volume of cooling liquid, relative to the total volume, is kept small. Moreover a miniaturization of the overall arrangement is achieved that permits use of the present invention to become very economical in mobile applications. In this regard a significant benefit is further enjoyed by the fact that, by virtue of the structure utilising the third dimension, a spatial separation of the power-conducting lines (or conductor rails) and terminals, on the one hand, and of the triggering lines, on the other hand, is made possible. This considerably enhances immunity to interference. A further significant aspect of the present invention is the modular structure, which permits problem-free expansion and adaptation of the half-bridge module in line with the particular requirements.
In a preferred embodiment the semiconductor switches are constituted by fast-switching, low-loss field-effect transistors (FETs) or by fast-switching, low-loss bipolar transistors with insulated gate terminal (IGBTs). In particular, MOSFETs with integrated freewheeling diodes or additional external freewheeling diodes connected to the transistors in parallel can be employed. These external freewheeling diodes are advantageously arranged in the same manner as the semiconductor switches and in the immediate vicinity of the latter on one of the conductor rails.
Electrically conducting spacers are arranged on the first and third conductor rails, in particular for the mechanical and electrical parallel connection of several half-bridge modules. Hence half-bridge modules of the same type can be rigidly coupled to one another, and at the same time the supply of the high and low potentials to all the half-bridge modules that have been coupled in such a manner can be achieved in a straightforward way. In one embodiment of the present invention the spacers are realised as separate components, with which the respective conductor rails are connected (screw-coupled, riveted, welded etc). As an alternative to this, the spacers may also be integral with the conductor rails, so that the requisite spacing between the individual half-bridge modules comes about and is also kept constant by a direct joining of the respective conductor rails.
In a preferred embodiment of the present invention the first, second and third conductor rails are firmly connected to one another mechanically by an electrically insulating carrier board. As an alternative to this, the first, second and third conductor rails may be firmly connected to one another mechanically by electrically insulating crossmembers which are arranged between the individual conductor rails. The carrier board may also serve to receive conductor tracks in order to supply control signals to the semiconductors or in order to lead out test points or measuring points. The carrier board also serves to receive interconnecting lines between the respective control inputs of the semiconductor switches and the terminal for connection to the triggering device.
In this case the carrier board is preferably provided with recesses which are dimensioned in such a way that the semiconductors (transistors and diodes) that are directly applied on the conductor rails are exposed at least with their contacting pointsxe2x80x94that is, they are not covered up by the carrier board. This has the result that the effective overall heights of the semiconductors and of the carrier board are not added. Rather, both are connected directly (at the same level) to the conductor rails. Hence the carrier board serves both for the mechanical connection of the conductor rails amongst themselves and for the electrical wiring arrangement. The connection of the conductor tracks that are arranged on the carrier board to the contacting points of the semiconductors is preferably established by bonding wires.
As an alternative to this, instead of the carrier board, an electrically insulating foil is arranged in the conducting rails, with interconnecting lines between the respective control inputs and the terminal for connection to the triggering device. Since a foil is not suitable to establish a mechanically rigid or firm connection between the individual conductor rails, with a view to producing the necessary strength of the conductor-rail arrangement an additional connection should be formed on the lateral faces of the conductor rails facing one another. This can be achieved by means of the aforementioned crossmembers or by means of an electrically insulating adhesive.
In a preferred embodiment of the present invention the electrically insulating carrier board or the foil carries current-limiting resistors in the triggering lines for the semiconductor switches, said (gate) resistors being provided between the respective control inputs and the terminal for connection to the triggering device.
In accordance with the present invention, at least two half-bridge modules of the type described above are assigned to one another mechanically and are electrically connected in parallel in order to form a half-bridge arrangement. By virtue of the modular concept according to the present invention an increase in power output is easily achieved. By a simple parallel connection of an appropriate number of half-bridge modules or an expansion of a half-bridge arrangement through additional half-bridge modules it is also possible to provide a higher power output or to increase the number of phases.
Accordingly, the present invention also relates to a power output stage of a triggering device for a multiphase electric motor, wherein a half-bridge arrangement is provided for each phase of the electric motor, the half-bridge arrangements being arranged alongside one another. In a preferred embodiment of the present invention a power output stage of a triggering device for a multiphase electric motor is provided, a control-electronics module being spatially assigned to the power output stage and arranged in the same housing. By this arrangement both the control-electronics module and the power output stage with their plurality of half-bridge arrangements or half-bridge modules are accommodated in the same cooling medium. This creates a particularly compact structure of a functional overall arrangement, and the control lines may also be routed so as to be very short and rendering them less susceptible to interference.
The semiconductors that are used within the invention are preferably constituted by fast-switching, low-loss field-effect transistors (FETS) or by fast-switching, low-loss bipolar transistors with insulated gate terminal (IGBTs). In this case several pairs of semiconductor switches connected in series may be connected in parallel. In addition, the semiconductor switches may be constituted by a large number of individual semiconductor-switch modules with, in each case, low switching capacities. Through the use of many semiconductor-switch elements with, in each case, a relatively low switching capacity which are, however, easy to connect in parallel, effective cooling can be achieved, since the many individual components can be reached well by the cooling medium.